1. Field of the Invention
The present invention relates to systems and methods for controlling gear rattle by substantially eliminating backlash in a planetary gear set.
2. Background Art
Mating gear teeth in a pair of gears have an inherent amount of backlash attributable to clearance required to accommodate manufacturing variation and thermal expansion, which may allow an unacceptable amount of rattle during operation, particularly when experiencing frequent torque reversals between left and right hand (also referred to as clockwise/counter clockwise, positive/negative, drive/coast, or forward/reverse) torques. Prior art solutions to this problem include reduction or elimination of backlash by varying the center distance between gears or changing tooth thickness. One solution to eliminating backlash in external gears is disclosed in U.S. Pat. No. 4,688,441 in which one of the gears is split axially into two parts that are under spring load, rotatable relative to each other. One part of the split gear maintains tight contact against the driving face of the mating gear, and the other part against the coasting face. To eliminate backlash, the spring preload has to be at least as large as the maximum load that will be imposed upon the spring during operation of the gear. This solution is applied to non-planetary type gears and requires one of the gears to be axially split.
To reduce backlash related rattle in a planetary type gear set as disclosed in U.S. Pat. No. 4,799,396, a planetary gear set includes an output shaft rotatably supporting two planet gears engaging an internal gear fixed to a housing and a sun gear at the end of the input shaft. Supports for the planet gears are circumferentially movable during a manual adjustment procedure with respect to each other in order to eliminate backlash. Similarly, U.S. Pat. No. 6,099,432 describes a planetary gear set having a divided-type carrier that can be twisted using axial holes to manually adjust for backlash during or after assembly. Manually adjusting backlash as described in these disclosures may result in additional noise and produce high internal stresses related to gear run-out and an associate tight contact or binding condition during subsequent operation.
U.S. Pat. No. 5,098,359 discloses a reduction gear assembly having low elasticity between planet gears to provide elastic compliance between input and output members in forward as well as backward directions of torque transmission. The low elasticity in both forward and backward directions could lead to unacceptable vibrational resonance if the input or output is subjected to torsional vibrations. U.S. Published App. No. 2003/0073537 discloses a differential planetary gear system having an additional planetary gear at each position, an additional ring gear and a pre-load mechanism to reduce backlash.